[IA64] rework memory attribute aliasing

	         MEMORY ATTRIBUTE ALIASING ON IA-64

			   Bjorn Helgaas

		       <bjorn.helgaas@hp.com>

			    May 4, 2006

MEMORY ATTRIBUTES

    Itanium supports several attributes for virtual memory references.

    The attribute is part of the virtual translation, i.e., it is

    contained in the TLB entry.  The ones of most interest to the Linux

    kernel are:

	WB		Write-back (cacheable)

	UC		Uncacheable

	WC		Write-coalescing

    System memory typically uses the WB attribute.  The UC attribute is

    used for memory-mapped I/O devices.  The WC attribute is uncacheable

    like UC is, but writes may be delayed and combined to increase

    performance for things like frame buffers.

    The Itanium architecture requires that we avoid accessing the same

    page with both a cacheable mapping and an uncacheable mapping[1].

    The design of the chipset determines which attributes are supported

    on which regions of the address space.  For example, some chipsets

    support either WB or UC access to main memory, while others support

    only WB access.

MEMORY MAP

    Platform firmware describes the physical memory map and the

    supported attributes for each region.  At boot-time, the kernel uses

    the EFI GetMemoryMap() interface.  ACPI can also describe memory

    devices and the attributes they support, but Linux/ia64 currently

    doesn't use this information.

    The kernel uses the efi_memmap table returned from GetMemoryMap() to

    learn the attributes supported by each region of physical address

    space.  Unfortunately, this table does not completely describe the

    address space because some machines omit some or all of the MMIO

    regions from the map.

    The kernel maintains another table, kern_memmap, which describes the

    memory Linux is actually using and the attribute for each region.

    This contains only system memory; it does not contain MMIO space.

    The kern_memmap table typically contains only a subset of the system

    memory described by the efi_memmap.  Linux/ia64 can't use all memory

    in the system because of constraints imposed by the identity mapping

    scheme.

    The efi_memmap table is preserved unmodified because the original

    boot-time information is required for kexec.

KERNEL IDENTITY MAPPINGS

    Linux/ia64 identity mappings are done with large pages, currently

    either 16MB or 64MB, referred to as "granules."  Cacheable mappings

    are speculative[2], so the processor can read any location in the

    page at any time, independent of the programmer's intentions.  This

    means that to avoid attribute aliasing, Linux can create a cacheable

    identity mapping only when the entire granule supports cacheable

    access.

    Therefore, kern_memmap contains only full granule-sized regions that

    can referenced safely by an identity mapping.

    Uncacheable mappings are not speculative, so the processor will

    generate UC accesses only to locations explicitly referenced by

    software.  This allows UC identity mappings to cover granules that

    are only partially populated, or populated with a combination of UC

    and WB regions.

USER MAPPINGS

    User mappings are typically done with 16K or 64K pages.  The smaller

    page size allows more flexibility because only 16K or 64K has to be

    homogeneous with respect to memory attributes.

POTENTIAL ATTRIBUTE ALIASING CASES

    There are several ways the kernel creates new mappings:

    mmap of /dev/mem

	This uses remap_pfn_range(), which creates user mappings.  These

	mappings may be either WB or UC.  If the region being mapped

	happens to be in kern_memmap, meaning that it may also be mapped

	by a kernel identity mapping, the user mapping must use the same

	attribute as the kernel mapping.

	If the region is not in kern_memmap, the user mapping should use

	an attribute reported as being supported in the EFI memory map.

	Since the EFI memory map does not describe MMIO on some

	machines, this should use an uncacheable mapping as a fallback.

    mmap of /sys/class/pci_bus/.../legacy_mem

	This is very similar to mmap of /dev/mem, except that legacy_mem

	only allows mmap of the one megabyte "legacy MMIO" area for a

	specific PCI bus.  Typically this is the first megabyte of

	physical address space, but it may be different on machines with

	several VGA devices.

	"X" uses this to access VGA frame buffers.  Using legacy_mem

	rather than /dev/mem allows multiple instances of X to talk to

	different VGA cards.

	The /dev/mem mmap constraints apply.

	However, since this is for mapping legacy MMIO space, WB access

	does not make sense.  This matters on machines without legacy

	VGA support: these machines may have WB memory for the entire

	first megabyte (or even the entire first granule).

	On these machines, we could mmap legacy_mem as WB, which would

	be safe in terms of attribute aliasing, but X has no way of

	knowing that it is accessing regular memory, not a frame buffer,

	so the kernel should fail the mmap rather than doing it with WB.

    read/write of /dev/mem

	This uses copy_from_user(), which implicitly uses a kernel

	identity mapping.  This is obviously safe for things in

	kern_memmap.

	There may be corner cases of things that are not in kern_memmap,

	but could be accessed this way.  For example, registers in MMIO

	space are not in kern_memmap, but could be accessed with a UC

	mapping.  This would not cause attribute aliasing.  But

	registers typically can be accessed only with four-byte or

	eight-byte accesses, and the copy_from_user() path doesn't allow

	any control over the access size, so this would be dangerous.

    ioremap()

	This returns a kernel identity mapping for use inside the

	kernel.

	If the region is in kern_memmap, we should use the attribute

	specified there.  Otherwise, if the EFI memory map reports that

	the entire granule supports WB, we should use that (granules

	that are partially reserved or occupied by firmware do not appear

	in kern_memmap).  Otherwise, we should use a UC mapping.

PAST PROBLEM CASES

    mmap of various MMIO regions from /dev/mem by "X" on Intel platforms

      The EFI memory map may not report these MMIO regions.

      These must be allowed so that X will work.  This means that

      when the EFI memory map is incomplete, every /dev/mem mmap must

      succeed.  It may create either WB or UC user mappings, depending

      on whether the region is in kern_memmap or the EFI memory map.

    mmap of 0x0-0xA0000 /dev/mem by "hwinfo" on HP sx1000 with VGA enabled

      See https://bugzilla.novell.com/show_bug.cgi?id=140858.

      The EFI memory map reports the following attributes:

        0x00000-0x9FFFF WB only

        0xA0000-0xBFFFF UC only (VGA frame buffer)

        0xC0000-0xFFFFF WB only

      This mmap is done with user pages, not kernel identity mappings,

      so it is safe to use WB mappings.

      The kernel VGA driver may ioremap the VGA frame buffer at 0xA0000,

      which will use a granule-sized UC mapping covering 0-0xFFFFF.  This

      granule covers some WB-only memory, but since UC is non-speculative,

      the processor will never generate an uncacheable reference to the

      WB-only areas unless the driver explicitly touches them.

    mmap of 0x0-0xFFFFF legacy_mem by "X"

      If the EFI memory map reports this entire range as WB, there

      is no VGA MMIO hole, and the mmap should fail or be done with

      a WB mapping.

      There's no easy way for X to determine whether the 0xA0000-0xBFFFF

      region is a frame buffer or just memory, so I think it's best to

      just fail this mmap request rather than using a WB mapping.  As

      far as I know, there's no need to map legacy_mem with WB

      mappings.

      Otherwise, a UC mapping of the entire region is probably safe.

      The VGA hole means the region will not be in kern_memmap.  The

      HP sx1000 chipset doesn't support UC access to the memory surrounding

      the VGA hole, but X doesn't need that area anyway and should not

      reference it.

    mmap of 0xA0000-0xBFFFF legacy_mem by "X" on HP sx1000 with VGA disabled

      The EFI memory map reports the following attributes:

        0x00000-0xFFFFF WB only (no VGA MMIO hole)

      This is a special case of the previous case, and the mmap should

      fail for the same reason as above.

NOTES

    [1] SDM rev 2.2, vol 2, sec 4.4.1.

    [2] SDM rev 2.2, vol 2, sec 4.4.6.

 * Copyright (C) 1999-2003 Hewlett-Packard Co.

 *	David Mosberger-Tang <davidm@hpl.hp.com>

 *	Stephane Eranian <eranian@hpl.hp.com>

 * (c) Copyright 2006 Hewlett-Packard Development Company, L.P.

 *	Bjorn Helgaas <bjorn.helgaas@hp.com>

 *

 * All EFI Runtime Services are not implemented yet as EFI only

 * supports physical mode addressing on SoftSDV. This is to be fixed

	return 0;

}

static efi_memory_desc_t *

efi_memory_descriptor (unsigned long phys_addr)

static struct kern_memdesc *

kern_memory_descriptor (unsigned long phys_addr)

{

	void *efi_map_start, *efi_map_end, *p;

	efi_memory_desc_t *md;

	u64 efi_desc_size;

	efi_map_start = __va(ia64_boot_param->efi_memmap);

	efi_map_end   = efi_map_start + ia64_boot_param->efi_memmap_size;

	efi_desc_size = ia64_boot_param->efi_memdesc_size;

	struct kern_memdesc *md;

	for (p = efi_map_start; p < efi_map_end; p += efi_desc_size) {

		md = p;

		if (phys_addr - md->phys_addr < (md->num_pages << EFI_PAGE_SHIFT))

	for (md = kern_memmap; md->start != ~0UL; md++) {

		if (phys_addr - md->start < (md->num_pages << EFI_PAGE_SHIFT))

			 return md;

	}

	return 0;

}

static int

efi_memmap_has_mmio (void)

static efi_memory_desc_t *

efi_memory_descriptor (unsigned long phys_addr)

{

	void *efi_map_start, *efi_map_end, *p;

	efi_memory_desc_t *md;

	for (p = efi_map_start; p < efi_map_end; p += efi_desc_size) {

		md = p;

		if (md->type == EFI_MEMORY_MAPPED_IO)

			return 1;

		if (phys_addr - md->phys_addr < (md->num_pages << EFI_PAGE_SHIFT))

			 return md;

	}

	return 0;

}

}

EXPORT_SYMBOL(efi_mem_attributes);

/*

 * Determines whether the memory at phys_addr supports the desired

 * attribute (WB, UC, etc).  If this returns 1, the caller can safely

 * access size bytes at phys_addr with the specified attribute.

 */

int

efi_mem_attribute_range (unsigned long phys_addr, unsigned long size, u64 attr)

u64

efi_mem_attribute (unsigned long phys_addr, unsigned long size)

{

	unsigned long end = phys_addr + size;

	efi_memory_desc_t *md = efi_memory_descriptor(phys_addr);

	u64 attr;

	/*

	 * Some firmware doesn't report MMIO regions in the EFI memory

	 * map.  The Intel BigSur (a.k.a. HP i2000) has this problem.

	 * On those platforms, we have to assume UC is valid everywhere.

	 */

	if (!md || (md->attribute & attr) != attr) {

		if (attr == EFI_MEMORY_UC && !efi_memmap_has_mmio())

			return 1;

	if (!md)

		return 0;

	}

	/*

	 * EFI_MEMORY_RUNTIME is not a memory attribute; it just tells

	 * the kernel that firmware needs this region mapped.

	 */

	attr = md->attribute & ~EFI_MEMORY_RUNTIME;

	do {

		unsigned long md_end = efi_md_end(md);

		if (end <= md_end)

			return 1;

			return attr;

		md = efi_memory_descriptor(md_end);

		if (!md || (md->attribute & attr) != attr)

		if (!md || (md->attribute & ~EFI_MEMORY_RUNTIME) != attr)

			return 0;

	} while (md);

	return 0;

}

u64

kern_mem_attribute (unsigned long phys_addr, unsigned long size)

{

	unsigned long end = phys_addr + size;

	struct kern_memdesc *md;

	u64 attr;

	/*

 * For /dev/mem, we only allow read & write system calls to access

 * write-back memory, because read & write don't allow the user to

 * control access size.

	 * This is a hack for ioremap calls before we set up kern_memmap.

	 * Maybe we should do efi_memmap_init() earlier instead.

	 */

	if (!kern_memmap) {

		attr = efi_mem_attribute(phys_addr, size);

		if (attr & EFI_MEMORY_WB)

			return EFI_MEMORY_WB;

		return 0;

	}

	md = kern_memory_descriptor(phys_addr);

	if (!md)

		return 0;

	attr = md->attribute;

	do {

		unsigned long md_end = kmd_end(md);

		if (end <= md_end)

			return attr;

		md = kern_memory_descriptor(md_end);

		if (!md || md->attribute != attr)

			return 0;

	} while (md);

	return 0;

}

EXPORT_SYMBOL(kern_mem_attribute);

int

valid_phys_addr_range (unsigned long phys_addr, unsigned long size)

{

	return efi_mem_attribute_range(phys_addr, size, EFI_MEMORY_WB);

}

	u64 attr;

	/*

 * We allow mmap of anything in the EFI memory map that supports

 * either write-back or uncacheable access.  For uncacheable regions,

 * the supported access sizes are system-dependent, and the user is

 * responsible for using the correct size.

 *

 * Note that this doesn't currently allow access to hot-added memory,

 * because that doesn't appear in the boot-time EFI memory map.

	 * /dev/mem reads and writes use copy_to_user(), which implicitly

	 * uses a granule-sized kernel identity mapping.  It's really

	 * only safe to do this for regions in kern_memmap.  For more

	 * details, see Documentation/ia64/aliasing.txt.

	 */

	attr = kern_mem_attribute(phys_addr, size);

	if (attr & EFI_MEMORY_WB || attr & EFI_MEMORY_UC)

		return 1;

	return 0;

}

int

valid_mmap_phys_addr_range (unsigned long phys_addr, unsigned long size)

{

	if (efi_mem_attribute_range(phys_addr, size, EFI_MEMORY_WB))

	/*

	 * MMIO regions are often missing from the EFI memory map.

	 * We must allow mmap of them for programs like X, so we

	 * currently can't do any useful validation.

	 */

	return 1;

}

	if (efi_mem_attribute_range(phys_addr, size, EFI_MEMORY_UC))

		return 1;

pgprot_t

phys_mem_access_prot(struct file *file, unsigned long pfn, unsigned long size,

		     pgprot_t vma_prot)

{

	unsigned long phys_addr = pfn << PAGE_SHIFT;

	u64 attr;

	return 0;

	/*

	 * For /dev/mem mmap, we use user mappings, but if the region is

	 * in kern_memmap (and hence may be covered by a kernel mapping),

	 * we must use the same attribute as the kernel mapping.

	 */

	attr = kern_mem_attribute(phys_addr, size);

	if (attr & EFI_MEMORY_WB)

		return pgprot_cacheable(vma_prot);

	else if (attr & EFI_MEMORY_UC)

		return pgprot_noncached(vma_prot);

	/*

	 * Some chipsets don't support UC access to memory.  If

	 * WB is supported, we prefer that.

	 */

	if (efi_mem_attribute(phys_addr, size) & EFI_MEMORY_WB)

		return pgprot_cacheable(vma_prot);

	return pgprot_noncached(vma_prot);

}

int __init

#include <linux/module.h>

#include <linux/efi.h>

#include <asm/io.h>

#include <asm/meminit.h>

static inline void __iomem *

__ioremap (unsigned long offset, unsigned long size)

void __iomem *

ioremap (unsigned long offset, unsigned long size)

{

	if (efi_mem_attribute_range(offset, size, EFI_MEMORY_WB))

		return phys_to_virt(offset);

	u64 attr;

	unsigned long gran_base, gran_size;

	if (efi_mem_attribute_range(offset, size, EFI_MEMORY_UC))

	/*

	 * For things in kern_memmap, we must use the same attribute

	 * as the rest of the kernel.  For more details, see

	 * Documentation/ia64/aliasing.txt.

	 */

	attr = kern_mem_attribute(offset, size);

	if (attr & EFI_MEMORY_WB)

		return phys_to_virt(offset);

	else if (attr & EFI_MEMORY_UC)

		return __ioremap(offset, size);

	/*

	 * Someday this should check ACPI resources so we

	 * can do the right thing for hot-plugged regions.

	 * Some chipsets don't support UC access to memory.  If

	 * WB is supported for the whole granule, we prefer that.

	 */

	gran_base = GRANULEROUNDDOWN(offset);

	gran_size = GRANULEROUNDUP(offset + size) - gran_base;

	if (efi_mem_attribute(gran_base, gran_size) & EFI_MEMORY_WB)

		return phys_to_virt(offset);

	return __ioremap(offset, size);

}

EXPORT_SYMBOL(ioremap);

void __iomem *

ioremap_nocache (unsigned long offset, unsigned long size)

{

	if (kern_mem_attribute(offset, size) & EFI_MEMORY_WB)

		return 0;

	return __ioremap(offset, size);

}

EXPORT_SYMBOL(ioremap_nocache);

int

pci_mmap_legacy_page_range(struct pci_bus *bus, struct vm_area_struct *vma)

{

	unsigned long size = vma->vm_end - vma->vm_start;

	pgprot_t prot;

	char *addr;

	/*

	 * Avoid attribute aliasing.  See Documentation/ia64/aliasing.txt

	 * for more details.

	 */

	if (!valid_mmap_phys_addr_range(vma->vm_pgoff << PAGE_SHIFT, size))

		return -EINVAL;

	prot = phys_mem_access_prot(NULL, vma->vm_pgoff, size,

				    vma->vm_page_prot);

	if (pgprot_val(prot) != pgprot_val(pgprot_noncached(vma->vm_page_prot)))

		return -EINVAL;

	addr = pci_get_legacy_mem(bus);

	if (IS_ERR(addr))

		return PTR_ERR(addr);

	vma->vm_pgoff += (unsigned long)addr >> PAGE_SHIFT;

	vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot);

	vma->vm_page_prot = prot;

	vma->vm_flags |= (VM_SHM | VM_RESERVED | VM_IO);

	if (remap_pfn_range(vma, vma->vm_start, vma->vm_pgoff,

			    vma->vm_end - vma->vm_start, vma->vm_page_prot))

			    size, vma->vm_page_prot))

		return -EAGAIN;

	return 0;

}

#define ARCH_HAS_VALID_PHYS_ADDR_RANGE

extern u64 kern_mem_attribute (unsigned long phys_addr, unsigned long size);

extern int valid_phys_addr_range (unsigned long addr, size_t count); /* efi.c */

extern int valid_mmap_phys_addr_range (unsigned long addr, size_t count);